Our long-term goal is to characterize the molecular mechanisms and biological impact of chemokine receptor signaling in T lymphocytes. Toward this end, we are studying the role and mechanisms of function of the CXCR4 chemokine receptor in T cells. CXCR4 stimulates the proliferation and/or apoptosis of several cell types, and mutant mice lacking either CXCR4 or its ligand, SDF-1, die from developmental defects. In addition, CXCR4 binds directly to the gp120 glycoprotein of Human Immunodeficiency Virus-1 (HIV-1) and, together with HIV-1 binding to CD4, permits viral infection of T lymphocytes. The molecular mechanisms by which CXCR4 mediates these effects are poorly understood. Our preliminary results indicate that CXCR4 signaling uses a Gi protein to activate the ERK mitogen-activated protein (MAP) kinases in T lymphocytes. ERK and other MAP kinases phosphorylate transcription factors in response to signaling by cell-surface receptors, thereby allowing growth factors and hormones to regulate cell growth and differentiation. Our central hypothesis is that chemokine receptors use distinct G proteins, small GTP-binding proteins and kinases to activate ERK in T lymphocytes. Therefore, our specific aims are to: 1) characterize CXCR4-mediated stimulation of MEK-1 and ERK, 2) characterize CXCR4 coupling to G proteins that mediate ERK activation, and 3) characterize the role(s) of lck and CD4 in CXCR4 activation of ERK. We propose to use state-of-the-art molecular techniques in combination with normal human T cells and T cell model cell lines to characterize the molecular mechanisms of CXCR4-mediated ERK activation. We are optimistic that the successful completion of this proposal will characterize in detail the molecular mechanism(s) used by CXCR4 to activate ERK in an important cell type where CXCR4 is abundantly expressed: T lymphocytes. Since ERK participates in T lymphocyte differentiation and immune activation, the results of these studies will form a basis for understanding chemokine control of the immune system's development and function. In addition, understanding T lymphocyte CXCR4 signaling will provide the theoretical framework for future studies aimed at understanding the pathophysiology of AIDS.